Albert II abdicated on Sunday after 20 years as 'King of the Belgians' in favour of his son Philippe, who becomes the seventh monarch of a country split between its French and Flemish speaking halves.

Albert II abdicated on Sunday after 20 years as 'King of the Belgians' in favour of his son Philippe, who becomes the seventh monarch of a country split between its French and Flemish speaking halves.

In a solemn ceremony at the royal palace, Albert signed the act of abdication in front of an audience of some 250 local dignitaries and political leaders, thanking them for working for the country and holding Belgium together.

Philippe will be sworn in as king at midday (1000 GMT) before parliament, with a day of pageantry and celebration attracting large crowds onto the streets outside the royal palace in central Brussels in brilliant sunny weather.

As Queen Paola held back tears, Albert said he simply wanted to tell her "thank you ... and a big kiss," a typically human touch for a man credited with the ability to reach out to people.

In a short address, he also said he wanted to pay "special homage" to Prime Minister Elio Di Rupo who had accepted the "heavy task of forming a government (in 2011)" when the country appeared rudderless after inconclusive polls the previous year.

Di Rupo and his government had taken "the indispensable measures needed to promote the well-being of all," the king said, stressing the key achievement of keeping the country together.

Albert expressed too his full confidence in Philippe, saying "you have all the qualities needed to serve your country well.

King Albert II of Belgium (L) arrives with his son Crown Prince Philippe to attend a concert celebrating King Albert's 20th anniversary of reign on the eve of Belgian National Day, King Albert II's abdication and the inauguration of his successor King Philippe, at the Beaux-Arts theatre in Brussels. (Reuters Photo)

"You and your dear wife Mathilde have all our confidence."

Born June 6, 1934, Albert was the second son of Leopold III and Queen Astrid but succeeded to the throne on August 9, 1993 after the unexpected death of his brother, King Baudouin, who was childless.

Earlier this month, he announced he would step down because age and ill-health prevented him from fulfilling his royal duties as he would like.